The invention relates to a circuit arrangement for temperature-dependent voltage regulation of control voltages required in the operation of piezo-electric recording nozzles of ink mosaic recording devices.
Circuit arrangements of this type may comprise a control circuit which is assigned to each recording nozzle and contains a voltage transformer circuit whose secondary inductance, together with the capacitance of the recording nozzle, form an oscillating circuit, and which also contains means for setting the specific control voltage.
Ink mosaic recording devices utilizing recording nozzles which operate in accordance with the piezo-electric principle have utilized tubular drive elements of polarized ceramic, which contain the recording fluid and whose diameter is constricted when an electric voltage, corresponding to the polarization voltage, is connected thereto and expands when an electric voltage opposite to the polarity voltage is connected.
Circuit arrangements are known for the production of the voltages required in the controlling of recording nozzles, for example such as illustrated in U.S. Pat. No. 4,161,670 corresponding to German OS No. 25 48 691, in which the recording nozzles are expanded from a rest state by the connection of a voltage opposed to the polarity voltage, which expanded state is maintained for a predetermined length of time, and the droplet of ink subsequently ejected from the recording nozzle, which is brought from such an expanded state into a constricted state as a result of a change in polarity in the control voltage which produced the expanded state.
In such known circuit arrangement, there is provided for this purpose a voltage transformer circuit whose secondary-inductance, together with the capacitance of the recording nozzle, forms an oscillating circuit which is attenuated over an attenuating element. The level of the control voltage applied to the recording nozzles is determined by suitable means which is operative to limit the primary current in the voltage transformer circuit. This known method of driving the recording nozzles has the advantage that a very wide voltage range can be produced with relatively small changes in voltage in the ceramic tube of the recording nozzle. In addition, the control voltage for the recording nozzles can be individually set with respect to each recording nozzle, which is of particular advantage in ink mosaic recording devices in which the recording head contains a plurality of recording nozzles. In this case, a separate control circuit is provided for each recording nozzle.
However, the mode of operation of the recording nozzles required for normal, satisfactory operation, is dependent not only upon a circuit employing specific, individually adjustable control voltages, but also it is equally dependent upon the viscosity of the recording liquid. The viscosity of the ink normally used as the recording liquid is strongly temperature dependent, and changes even in the presence of slight variations in the environmental temperature. Thus, in ink jet recorders in which ink is supplied under static pressure to a nozzle and continuously ejected therefrom in the form of ink droplets and accelerated under the influence of an electrostatic field produced between the nozzle and the electrodes, utilizing a high voltage generator, it has already proven desirable to monitor the ink temperature by means of a temperature sensor and modifying the output voltage of the high voltage generator in dependence thereon. Such a type of an arrangement is illustrated, for example, in U.S. Pat. No. 3,914,772, corresponding to German AS No. 23 53 525.
This arrangement, however, is not suitable for ink mosaic recording devices comprising recording nozzles operating in accordance with the piezo-electric principle, particularly in devices wherein each individual nozzle of the recording head must be supplied with an individual control voltage, and in which the control circuit utilized to produce the individually adjustable control voltages are each associated with the individual recording nozzles.